Estimating daily mean land surface albedo from MODIS data

Land surface albedo (LSA) is an important component of the surface radiation budget. For calculation of the surface shortwave net radiation budget, temporal mean albedo is more important than instantaneous albedo. Although Moderate Resolution Imaging Spectroradiometer (MODIS) albedo products have been extensively validated, little effort has been made to evaluate the accuracy of daily mean albedo from MODIS. In this study, we calculate daily mean albedo from MODIS data using a direct method and a look-up table (LUT) method. Comparison with in situ albedo measured at 27 field stations shows that both methods can estimate daily mean albedo with high accuracy. The root-mean-square error (RMSE) of snow-free daily mean albedo retrieved by the LUT method and the direct method is 0.033 and 0.034, respectively. Over the 12 spatially representative stations, RMSE of daily mean albedo is 0.022 and 0.023 by the LUT and direct approach, respectively. Simply using the local noon albedo value as a surrogate of daily mean albedo leads to overestimation of daily shortwave net radiation. By using the data of daily mean albedo, the bias in estimating daily shortwave net radiation can be reduced by 2.8 W/m2 with the direct method and 2.6 W/m2 with the LUT method, compared to the use of local noon albedo.